Method of making cast iron



ZSheetS-Sheet 1 May'z, v1967A Filed June 5, 1964 Fig 48 Fig. 2. 49

lNv-ENToR Carl George deLava|,Jr.

May 2, 1967 c. G. DE LAVAL, JR

METHOD 0F MAKING CAST IRON 2 shets-sheet 2 Filed June 5, 1964 INVEN'roR Carl George deLoval Jr.

United States Patent 3,317,310 METHOD OF MAKING CAST IRON Carl George deLaval, Jr., 21 Sunnyhill Drive,

Pittsburgh, Pa. 15228 Filed June 5, 1964, Ser. No. 372,914 7 Claims. (Cl. 7543) The present invention relates to an improved method for the manufacture of cast iron, its family of alloys, in-cluding ductile iron.

The method of the present invention provides 'a rapid and ellicient method for melting cast iron and for controlling the character of the product produced.

In accordance with the present invention, the charge is melted in a reverberatory furnace in which the conditions are carefully controllable. Reverberatory furnaces have the advantage that they can be heated rapidly to a high temperature, but in the past, it has not always been possible to take advantage of the high temperatures attainable with such a furnace, nor produce them economically. These factors, coupled with the inability to control the character of the atmosphere in the furnace have limited the usefulness of reverberatory furnaces in the casting of ferrous metals, particularly gray iron.

An object of the present invention is to provide an improved method of producing cast iron under readily controllable conditions.

A further object of the invention is to provide a method for producing cast iron under conditions such that undesirable elements are reduced in the nal product, while substantially preventing decarburization of the cast iron.

Still another object of the present invention is to provide a method of making cast iron which reduces the amount of heat loss previously encountered when cast iron was melted in a reverberatory furnace.

In accordance with the Ipresent invention, the charge to be melted is introduced into a reverberatory furnace, together with suicient acidic components to produce an acid slag. A substantially neutral combustion flame produced by the oxidation of natural gas or the like is directed against the material in the furnace under conditions resulting in the reflection of the heat of the flame to the portion of the stack at which the charge enters the furnace. In this way, the heat from the llame which would otherwise be radiated Iand lost by absorption into the refractory walls is utilized more efficiently. The treatment with the substantially neutral combustion llame is continued until melting of the charge has substantially commenced, whereupon the amount of oxygen in the llame is increased so that the atmosphere becomes substantially oxidizing. The remainder of the melting then occurs under substantially oxidizing conditions conducive to the formation of substantial amounts of ferrous oxide in the molten material. Upon completion of the melting, a major portion of the resultant acid acting slag is removed, and nally the molten material is superheated with a substantially neutral flame until the appropriate pouring temperature is reached and the cast iron is poured.

A further description of the present invention will be made in conjunction with the attached drawings which illustrate a preferred embodiment thereof.

FIGURE 1 is a side elevational view of a reverberatory furnace embodying the principles of the present invention;

FIGURE 2 is a side elevational view of the assembly shown in FIGURE l at right angles to the showing in FIGURE l;

FIGURE 3 is a cross-sectional view illustrating the interior construction of the furnace; and

FIGURE 4 is a cross-sectional View vtaken transversely of the furnace.

As shown on the drawings:

In FIGURE 1, reference numeral 10 indicates generally a pedestal which supports the Weight of the reverberatory furnace proper, generally indicated 'at numeral 11. Two pairs of spaced rollers 12 and 13 (see FIGURE 2) are mounted for the rotation on the pedestal 10 and support the furnace 11 for pivotal movement thereon. A pair of cylinders 14 secured to the pedestal 10 and pistons 16 pivotally secured to the body of the furnace 11 control the rocking movement of the furnace 11 about the rollers 12 and 13.

Turning now to the furnace interior, illustrated in FIG'URES 3 and 4 of the drawing it will be seen that the inlet to the furnace 11 consists of a charging stack 21 having an inclined wall surface 22 terminating in a stepped wall 23 over which the charge cascades in entering the interior of the furnace.

The floor of the furnace forms a hearth 24 upon which the molten metal accumulates in the form of a uniform, shallow layer of metal. For the melting of gray iron, it is denitely desirable that the hearth 24 be composed of an acidic refractory material, such as alumina-silica composition containing at least 50% by weight alumina. One suitable commercial composition is known as DV-38. Immediately below the hearth 24 in the form of the invention shown, is an intermediate layer 26 of a refractory material such as KX-99, super duty fireclay brick. In the form of the invention shown, the second layer beneath the hearth 24, an intermediate layer 27 may be composed of material such as Empire brick, a highly refractory high-duty iirebrick made from self-bonding high quality Missouri clays. The outer shell of the furnace, in the illustrated embodiment consists of a firebrick composition such as that known commercially as G-26, Iand insulating iirebrick made from Missouri lire-clay. This layer has been identified at reference numeral 28 in the drawings.

Immediately adjacent the inlet end of the charging stack 21 is a section 31 of a very refractory material such as silicon carbide overlaid by means of a castable refractory such as Remrney 3400 castable, the overlay being designated reference numeral 32.

The furnace construction may also include a typical arch generally designated at numeral 33 and composed of sections of a refractory material such as the aforementioned KX-99. The individual sections of the arch are held together by means of channels 34 which are secured together in compression by means of a spring 3-6 acting between the opposed channels 34.

An angularly disposed wall 37, preferably consisting of a cast structure of high alumina, castable refractory material such as Remmey 3400 castable is provided with one or more recesses 38 to accommodate the burner head structures which will be described in a succeeding portion of this specification. At this point, however, it is important to note that the axes of the burners are so arranged as to project the flame along a line 39 which intersects the hearth centrally of the furnace, and thereby reects the radiant heat from the flame along a line 41 to direct that heat at the throat of the charging stack. Thus, as the material cascades down the stepped portion 23, the additional radiant heat from the flame serves to intensify the heat at that point and provide for more eficient melting of the charge.

In the particular form of the invention illustrated in the drawings, the furnace assembly is provided with four burner heads 42, 43, 44 and 45. Fuel gas is introduced into the burner through a fuel gas manifold 46 connected to a suitable source of supply (not shown). For the purposes of this invention, it is preferable to use natural gas as the fuel because the free hydrogen in natural gas helps to reduce substantially the sulphur content of the final product.

Air is fed into the burners by means of a blower 47 driven by a motor 48. The blower 47 feeds an air manifold 49 which, in turn, delivers the air to the individual conduits 51, 52, 53, and 54 which feed the burners.

An auxiliary air supply is taken olf from the manifold 49 through conduit 56 controlled by a valve 57. The conduit 56 is directed into the furnace through a passage 55 as best illustrated in FIGURE 3 of the drawings. The function of the auxiliary air supply, as previously explained, is to provide an oxidizing atmosphere during at least a portion of the melting cycle.

As best seen in FIGURE 2, a slag door 59 and a molten metal spout 61 are provided on the front of the furnace to facilitate removal of slag and pouring of the metal. The slag door 59 covers the slag door opening 62 of the furnace, and the trough 61 communicates with a taphole 63 in the furnace, as illustrated in FIGURE 4.

A further description of the present invention will be made in conjunction with a specific example of the process here involved.

The initial charge of 2000 pounds to the furnace was made up of 1100 pounds of Sorel met-al, and 900 pounds of a foundry sprue. The compositions of the two materials are given in the following table:

Table l *lf/F4- C l Si Mn P S ,if Sorel metal (55%) 4. 25 0. 050 0. 540 0. 022 0.013 Foundry sprue (45%) 3. 60 2. 56 0. 009 0.183 0.125 Combine 3. 9 l. 2 0. 30 0. 097 0. 063

To initiate the operation of the furnace, the furnace was preheated with full burner fire for more than one hour, to produce a temperature in the refractory of 3000 F. or more. Natural gas was used as a fuel, with sufficient air being introduced to maintain the llame at a substantially neutral condition. The 2000 pound charge was then dropped into the furnace stack along with 50 pounds of silica sand and 5 ferrosilicon briquettes. In approximately one minute, the charge started melting and at that time the secondary air supply was introduced by opening the valve S7. In approximately twenty minutes, the charge was melted down and the valve 57 closed so that the oxidizing atmosphere was terminated. Within a few minutes after the secondary air supply was introduced, very brilliant sparklers emanated from the stack indicating that oxidation melting was taking place.

The slag door 59 was the opened and a rod inserted into the slag. The removed slag was tested by immersion in a solution of hydrochloric acid. No action took place on the slag, indicating that it was acidic, or at least nonbasic. Then, a major portion of the slag was removed through the slag door 59. Generally, it is preferable to remove about 70 to 80% of the slag at this time from the metal bath. Following this, the slag door 59 was closed and the gas burners were permitted to superheat the molten iron and remaining slag for a period of about ten minutes. At the time of slag removal, the temperature was about 2400 F., and this super-heating was carried out until the temperature of the molten iron was in the range of 2800 to 2850" F. For most purposes, the iron should be heated to within the range of 2700 to 2900 F. during this superheat. Finally, the remaining slag was drawn off, and the molten metal was poured through the pouring lip 61.

The analysis of the cast product obtained was as follows:

.Table Il C 3.64 Si 1.15 Mn 0.14 P 0.095 S 0.046

With the method of the present invention, it has been found possible to provide a higher grade melt from foundry scrap than has heretofore been achieved. The careful control of the conditions of melting made possible by the process of the present invention makes it possible to produce a product of controlled carbon content and substantially reduced sulphur content.

It will be evident that various modifications can be made to the described embodiment without departing from the scope of the present invention.

I claim:

1. The method of making cast iron which comprises introducing a cast iron forming charge into a reverberatory furnace together with sufcient acidic components to produce an acid slag, directing a substantially neutral combustion llame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed and then superheating the molten charge with a substantially neutral llame.

2. The method of making cast iron which comprises introducing a cast iron forming charge into a reverberatory furnace together with sufficient ferrosilicon and silica sand to produce an acid slag, directing a substantially neutral combustion llame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed, and then superheating the molten charge with a substantially neutral flame.

3. The method of making ycast iron which comprises preheating a reverberatory furnace until the refractories therein attained a temperature of about 3000 F., intro- `ducink a cast iron forming charge together with sufficient acidic components to produce an acid slag into the preheated furnace, directing a substantially neutral combustion llame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed, and then superheating the molten charge with a substantially neutral llame.

4. The method of making cast iron which comprises preheating a reverberatory furnace until the refractories therein attained a temperature of about 3000 F., introducing a cast iron forming charge together with sufficient acidic components to produce an acid slag into the preheated furnace, `directing a substantially neutral combustion llame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed, and then superheating the molten charge with a substantially neutral llame until the temperature of the molten material is in the range from about 2700 to 2900 F.

5. The method of making cast iron which comprises introducing a cast iron forming charge into a reverberatory furnace together with sufficient acidic components to produce an acid slag, directing a substantially neutral combustion llame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed, removing a major portion of the slag, and then superheating the molten material with a substantially neutral flame.

6. The method of making cast iron which comprises introducing a cast iron forming charge into a reverberatory furnace together with a suicient amount of ferrosilicon and silica sand to produce an acid slag, directing a substantially neutral flame at the charge in the furnace until melting of the charge commences, thereafter increasing the amount of oxygen in the furnace so that the furnace atmosphere becomes substantially oxidizing, continuing the application of the oxidizing atmosphere until the melting is completed, removing a major portion of the References Cited by the Examiner UNITED STATES PATENTS 1,140,550 5/ 1915 Weissenburger 75-60 10 2,226,967 12/ 1940 Chelius 75-43 X 2,671,724 3/ 1954 Kompart 75-43 2,755,180 7/1956 de Laval 75-43 2,786,748 3/ 1957 de Laval 75-43 15' DAVID L. RECK, Primm Examiner. H. W. TARRING, Assistant Examiner. 

1. THE METHOD OF MAKING CAST IRON WHICH COMPRISES INTRODUCING A CAST IRON FORMING CHARGE INTO A REVERBERATORY FURNACE TOGETHER WITH SUFFICIENT ACIDIC COMPONENTS TO PRODUCE AN ACID SLAG, DIRECTING A SUBSTANTIALLY NEUTRAL COMBUSTION FLAME AT THE CHARGE IN THE FURNACE UNTIL MELTING OF THE CHARGE COMMENCES, THEREAFTER INCREASING THE AMOUNT OF OXYGEN IN THE FURNACE SO THAT THE FURNACE ATMOSPHERE BECOMES SUBSTANTIALLY OXIDIZING, CONTINUING THE APPLICATION OF THE OXIDIZING ATMOSPHERE UNTIL THE MELTING IS COMPLETED AND THEN SUPERHEATING THE MOLTEN CHARGE WITH A SUBSTANTIALLY NEUTRAL FLAME. 